These studies are designed to evaluate the interaction of humoral antibodies with lymphocytes to affect tumor cell destruction. Emphases are placed on virally induced murine tumors and basic mechanisms of immune complex interaction with inflammatory cells. The divalent cation requirements for binding IgM and IgG immune complexes to lymphocyte subpopulations and macrophages are being studied. Antibody-dependent cell-mediated cytotoxicity against erythrocytes and tumor target cells can be mediated by thymus processed lymphocytes. Polyoma virus and murine sarcoma virus transformed cells are killed by thymocytes when antibodies having specificity for the appropriate virally determined cell surface antigen are used. Antibodies specific for embryonic antigens induces killing by thymocytes of MuSV, polyoma and SV40 transformed cells. Monoclonal IgM and antibody specific for M-MuSV, SRBC or TNP have been shown to induce cell-mediated killing by appropriately sensitized target cells. In vivo administration of IgM and anticarrier antibodies along with a hapten carrier conjugate potentiates the thymus dependent antibody response to the hapten.